U.S. patent application number 10/537799 was filed with the patent office on 2006-02-09 for distortion compensation device and distortion compensation method.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Takashi Enoki, Hideo Nagata.
Application Number | 20060029154 10/537799 |
Document ID | / |
Family ID | 33307845 |
Filed Date | 2006-02-09 |
United States Patent
Application |
20060029154 |
Kind Code |
A1 |
Nagata; Hideo ; et
al. |
February 9, 2006 |
Distortion compensation device and distortion compensation
method
Abstract
A compensation data table 304 generates baseband signal
nonlinear characteristic information. A determination section 305
determines from measured power whether power is on an upward trend
or on a downward trend. An IM unbalance compensation computation
section 306 generates an unbalance IM characteristic so that an
amplitude component and phase component when power is identical
differ when power is on an upward trend and when power is on a
downward trend, and generates a compensation signal of a
compensation characteristic that has an amplitude component and
phase component that are symmetrical with the generated unbalance
IM characteristic with respect to amplitude component and phase
component fixed values when there is a linear characteristic. A
complex multiplication section 307 combines the baseband signal
with the compensation signal. An amplifier 312 amplifies the
baseband signal and also suppresses distortion components generated
during amplification by means of the compensation signal. By this
means, distortion components in a state of lower/upper unbalance
can be suppressed with high precision.
Inventors: |
Nagata; Hideo; (Ogasa-gun,
JP) ; Enoki; Takashi; (Yokohama-shi, JP) |
Correspondence
Address: |
STEVENS, DAVIS, MILLER & MOSHER, LLP
1615 L. STREET N.W.
SUITE 850
WASHINGTON
DC
20036
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Osaka
JP
571-8501
|
Family ID: |
33307845 |
Appl. No.: |
10/537799 |
Filed: |
December 16, 2003 |
PCT Filed: |
December 16, 2003 |
PCT NO: |
PCT/JP03/16071 |
371 Date: |
June 7, 2005 |
Current U.S.
Class: |
375/296 |
Current CPC
Class: |
H04B 1/0475 20130101;
H03F 3/24 20130101; H04B 2001/0441 20130101; H03F 1/3223
20130101 |
Class at
Publication: |
375/296 |
International
Class: |
H04L 25/03 20060101
H04L025/03 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2002 |
JP |
2002-365447 |
Claims
1. A distortion compensation apparatus comprising: a power
calculation section that measures baseband signal power at
predetermined time intervals; a compensation computation section
that generates a compensation signal for suppressing distortion
components of said baseband signal so that a first phase component
and a first amplitude component when power is identical in said
compensation signal differ when current power measured by said
power calculation section is rising with respect to past power and
when current power measured by said power calculation section is
falling with respect to past power; a compensation signal combining
section that combines said compensation signal generated by said
compensation computation section with said baseband signal; and an
amplification section that suppresses with said compensation signal
said distortion components generated during amplification by
amplifying said baseband signal with which said compensation signal
is combined by said compensation signal combining section.
2. The distortion compensation apparatus according to claim 1,
wherein said compensation computation section detects said
distortion components that are nonlinear and for which a second
amplitude component and a second phase component when power is
identical in said distortion components differ when current power
measured by said power calculation section is rising with respect
to past power and when current power measured by said power
calculation section is falling with respect to past power, and
generates said compensation signal that has said first amplitude
component and said first phase component that are symmetrical to
said second amplitude component and said second phase component in
detected said distortion components with respect to a fixed value
of said second amplitude component and said second phase component
when said distortion components have a linear characteristic.
3. A transmitting apparatus provided with a distortion compensation
apparatus, said distortion compensation apparatus comprising: a
power calculation section that measures baseband signal power at
predetermined time intervals; a compensation computation section
that generates a compensation signal for suppressing distortion
components of said baseband signal so that a first phase component
and a first amplitude component when power is identical in said
compensation signal differ when current power measured by said
power calculation section is rising with respect to past power and
when current power measured by said power calculation section is
falling with respect to past power; a compensation signal combining
section that combines said compensation signal generated by said
compensation computation section with said baseband signal; and an
amplification section that suppresses with said compensation signal
said distortion components generated during amplification by
amplifying said baseband signal with which said compensation signal
is combined by said compensation signal combining section.
4. A distortion compensation method comprising: a step of measuring
baseband signal power at predetermined time intervals; a step of
generating a compensation signal for suppressing distortion
components of said baseband signal so that a first phase component
and a first amplitude component when power is identical in said
compensation signal differ when measured current power is rising
with respect to past measured power and when measured current power
is falling with respect to past measured power; a step of combining
generated said compensation signal with said baseband signal; and a
step of suppressing with said compensation signal said distortion
components generated during amplification by amplifying said
baseband signal with which said compensation signal is combined.
Description
TECHNICAL FIELD
[0001] The present invention relates to a distortion compensation
apparatus and distortion compensation method, and, for example, to
a distortion compensation apparatus and distortion compensation
method that eliminate distortion generated when a signal is
amplified.
BACKGROUND ART
[0002] Heretofore a predistortion distortion compensation apparatus
has been known as an apparatus that compensates for distortion
generated when a transmit signal is amplified in a radio
communication apparatus. FIG. 1 is a block diagram showing the
configuration of a conventional predistortion distortion
compensation apparatus 100.
[0003] Conventional predistortion distortion compensation apparatus
100 is composed of a baseband I input terminal 101, a baseband Q
input terminal 102, a power calculation section 103, a compensation
data table 104, a complex multiplication section 105, a
digital/analog converter (hereinafter referred to as "DAC") 106, a
DAC 107, a modulator (hereinafter referred to as "MOD") 108, an
oscillator 109, a power amplifier 110, and an RF output terminal
111.
[0004] In FIG. 1, a baseband I signal is input to baseband I input
terminal 101 and a baseband Q signal orthogonal to the I signal is
input to baseband Q input terminal 102, and these signals pass
through DAC 106 and DAC 107, and are modulated to RF signals by
despreading section 108. The signal modulated to RF then undergoes
power amplification by power amplifier 110 and is output from RF
output terminal 111.
[0005] At this time, since power amplifier 110 performs nonlinear
operation, distortion is generated in the signal amplified by power
amplifier 110. A predistortion function is a function for amending
the nonlinearity of power amplifier 110 to linearity. In order to
perform power amplifier 110 linearity compensation, compensation
data table 104 is provided with compensation data corresponding to
power values. Power calculation section 103 performs input baseband
signal power calculation every sampling time and outputs the result
to compensation data table 104. Compensation data table 104 is
referenced using the power calculation result input from power
calculation section 103, and the necessary compensation data is
extracted and output to complex multiplication section 105. Complex
multiplication section 105 operates so as to suppress distortion
generated in power amplifier 110 for the input I signal and Q
signal.
[0006] Due to various factors such as temperature characteristics,
the nonlinearity of power amplifier 110 differs even if the
measured power is the same when the measured power is on an upward
trend and when the measured power is on a downward trend.
[0007] FIG. 2 is a drawing showing signal components and distortion
components on the frequency axis when a transmit signal is
amplified. As shown in FIG. 2, when a transmit signal is composed
of two waves, a signal component #201 of frequency f1 and a signal
component #202 of frequency f2 (where f1<f2), a lower-side
(low-frequency side) distortion component #203 and upper-side
(high-frequency side) distortion component #204 are generated by
amplifying the transmit signal. In this case, distortion component
#203 level .beta. is greater than distortion component #204 level
.alpha., and lower/upper unbalance occurs in which the levels of
the low-frequency-side distortion component and high-frequency-side
distortion component on the frequency axis generated in the signal
amplified by power amplifier 110 are different.
[0008] However, a problem with a conventional distortion
compensation apparatus and distortion compensation method is that
the correspondence between power and compensation data is set in
compensation data table 104 without taking lower/upper unbalance
into consideration, and consequently distortion component #203 and
distortion component #204 in a state of lower/upper unbalance
cannot be suppressed with high precision.
DISCLOSURE OF INVENTION
[0009] It is an object of the present invention to provide a
distortion compensation apparatus and distortion compensation
method that enable distortion components in a state of lower/upper
unbalance to be suppressed with high precision.
[0010] This object can be achieved by generating a compensation
signal for suppressing baseband signal distortion components so
that the phase component and amplitude component when power is the
same in that compensation signal differs when the currently
measured power in the baseband signal is rising with respect to
power measured in the past and when the currently measured power in
the baseband signal is falling with respect to power measured in
the past.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 is a block diagram showing the configuration of a
conventional predistortion distortion compensation apparatus;
[0012] FIG. 2 is a drawing showing conventional signal components
and distortion components;
[0013] FIG. 3 is a block diagram showing the configuration of a
transmitting apparatus according to an embodiment of the present
invention;
[0014] FIG. 4 is a drawing showing the nonlinear relationship
between power and amplitude when there is no hysteresis in a power
amplifier according to an embodiment of the present invention;
[0015] FIG. 5 is a drawing showing the nonlinear relationship
between power and phase when there is no hysteresis in a power
amplifier according to an embodiment of the present invention;
[0016] FIG. 6 is a drawing showing the relationship between power
and amplitude when there is hysteresis in a power amplifier
according to an embodiment of the present invention;
[0017] FIG. 7 is a drawing showing the relationship between power
and phase when there is hysteresis in a power amplifier according
to an embodiment of the present invention;
[0018] FIG. 8 is a drawing showing the relationship between power
and amplitude in a compensation signal according to an embodiment
of the present invention;
[0019] FIG. 9 is a drawing showing the relationship between power
and phase in a compensation signal according to an embodiment of
the present invention;
[0020] FIG. 10 is a drawing showing the relationship between power
and amplitude in a compensation signal according to an embodiment
of the present invention; and
[0021] FIG. 11 is a drawing showing the relationship between power
and phase in a compensation signal according to an embodiment of
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0022] With reference now to the accompanying drawings, an
embodiment of the present invention will be explained in detail
below.
[0023] FIG. 3 is a block diagram showing the configuration of a
transmitting apparatus 300 according to an embodiment of the
present invention. In FIG. 3, transmitting apparatus 300 is mainly
composed of an input terminal 301, an input terminal 302, a power
calculation section 303, a compensation data table 304, a
determination section 305, an IM unbalance compensation computation
section 306, a complex multiplication section 307, a DAC 308, a DAC
309, an oscillator 310, a MOD 311, an amplifier 312, and an antenna
313.
[0024] Input terminal 301, input terminal 302, power calculation
section 303, compensation data table 304, determination section
305, IM unbalance compensation computation section 306, complex
multiplication section 307, DAC 308, DAC 309, oscillator 310, MOD
311, and amplifier 312 make up a distortion compensation apparatus
314. For distortion compensation apparatus 314 in FIG. 3, a
predistortion distortion compensation apparatus configuration is
shown, with power calculation section 303, compensation data table
304, determination section 305, IM unbalance compensation
computation section 306, and complex multiplication section 307
forming a predistortion function.
[0025] Input terminal 301 receives an I component baseband signal
and sends this signal to power calculation section 303 and complex
multiplication section 307.
[0026] Input terminal 302 receives a Q component baseband signal
and sends this signal to power calculation section 303 and complex
multiplication section 307.
[0027] Power calculation section 303 performs power calculations
for baseband signals input from input terminal 301 and input
terminal 302 every sampling time, and outputs measured power
information, which is calculated power information, to compensation
data table 304 and determination section 305.
[0028] Compensation data table 304 vector information comprises a
data table of amplifier 312 that has nonlinear characteristics.
Then compensation data table 304 outputs amplifier 312 nonlinear
characteristic information to IM unbalance compensation computation
section 306 based on measured power information input from power
calculation section 303 and the data table in compensation data
table 304. Nonlinear characteristic information held by
compensation data table 304 as vector information is the same as
nonlinear characteristic information held by data table 104 as
vector information.
[0029] Using at least two items of measured power information in
the measured power information for each sampling time input from
power calculation section 303, determination section 305 determines
whether measured power according to the latest measured power
information is rising or falling in comparison with measured power
according to past measured power information, and outputs the
determination result to IM unbalance compensation computation
section 306.
[0030] IM unbalance compensation computation section 306, which is
the compensation computation section, generates a compensation
signal based on nonlinear characteristic information found at at
least two different times input from compensation data table 304, a
coefficient, the result of determination by determination section
305 as to whether measured power is on an upward trend or on a
downward trend, and a fixed value when amplifier 312 is assumed to
have a linear characteristic--that is, when the amplifier performs
fixed transmission operation regardless of input power. IM
unbalance compensation computation section 306 then outputs the
generated compensation signal to complex multiplication section
307. The method of determining the compensation signal will be
described later herein.
[0031] Complex multiplication section 307, which is the
compensation signal combining section, suppresses baseband signal
distortion components based on the baseband signals input from
input terminal 301 and input terminal 302 and the compensation
signal input from IM unbalance compensation computation section
306, and outputs the resulting signals to DAC 308 and DAC 309.
[0032] DAC 308 converts the baseband signal input from complex
multiplication section 307 from analog data to digital data, and
outputs this digital data to MOD 311.
[0033] DAC 309 converts the baseband signal input from complex
multiplication section 307 from analog data format to digital data
format and generates a digital converted signal, and outputs this
signal to MOD 311.
[0034] Oscillator 310 is a local oscillator that outputs a
predetermined frequency signal to MOD 311.
[0035] MOD 311 modulates digital converted signals input from DAC
308 and DAC 309 using a signal input from oscillator 310 and
generates a modulated signal, and outputs this modulated signal to
amplifier 312.
[0036] Amplifier 312 amplifies the modulated signal input from MOD
311 and sends the amplified signal to antenna 313.
[0037] Next, the operation of transmitting apparatus 300 when
distortion component #203 and distortion component #204 shown in
FIG. 2 are suppressed will be described using FIG. 4 through FIG.
11.
[0038] A baseband signal is input to power calculation section 303
and complex multiplication section 307 as orthogonal data composed
of an I component and a Q component. Power calculation section 303
calculates power from the input baseband signals. Then compensation
data table 304 outputs amplifier 312 nonlinear characteristic
information to IM unbalance compensation computation section 306.
At this time, the relationship between amplitude and power shown in
FIG. 4 is stored in compensation data table 304. In addition, the
relationship between phase and power shown in FIG. 5 is stored in
compensation data table 304.
[0039] IM unbalance compensation computation section 306 has a
function of performing computational processing of input amplifier
312 nonlinear characteristic information so as to show the actual
unbalance IM characteristic, and a function of converting from the
obtained unbalance IM characteristic to a compensation
characteristic for linear output by amplifier 312 and generating a
compensation signal.
[0040] When performing computational processing to show the
unbalance IM characteristic, IM unbalance compensation computation
section 306 finds the unbalance IM characteristic based on
information on the nonlinear characteristic at time t-1 input from
compensation data table 304, information on the nonlinear
characteristic at time t after the elapse of a predetermined time
from time t-1 input from compensation data table 304, a
coefficient, the result of determination by determination section
305 as to whether measured power is on an upward trend or on a
downward trend, and a fixed value.
[0041] Specifically, the unbalance IM characteristic can be found
using Equation (1) or Equation (2).
Real.sub.--amp(t)=amp(t)+(amp(t)-amp(t-1)).times.(Li.sub.--amp-amp(t-1)).-
times.g (1)
Real.sub.--amp(t)=amp(t)-(amp(t)-amp(t-1)).times.(Li.sub.--amp-amp(t-1)).-
times.g (2) where [0042] Real_amp(t): Unbalance IM characteristic
at time t [0043] amp(t): Nonlinear characteristic at time t [0044]
amp(t-1): Nonlinear characteristic at time t-1 [0045] Li_amp: Fixed
value [0046] g: Coefficient
[0047] In this way, IM unbalance compensation computation section
306 finds the unbalance IM characteristic shown in FIG. 6 from the
amplifier 312 nonlinear characteristic shown in FIG. 4, and also
finds the unbalance IM characteristic shown in FIG. 7 from the
amplifier 312 nonlinear characteristic shown in FIG. 5. As shown in
FIG. 6, the relationship between amplitude and power in the
unbalance IM characteristic has hysteresis whereby the relationship
#601 between power and amplitude when power is on an upward trend
and the relationship #602 between power and amplitude when power is
on a downward trend follow different paths. Also, as shown in FIG.
7, the relationship between phase and power in the unbalance IM
characteristic has hysteresis whereby the relationship #701 between
power and phase when power is on an upward trend and the
relationship #702 between power and phase when power is on a
downward trend follow different paths. The relationship between
power and amplitude and the relationship between power and phase
when there is hysteresis of this kind can be changed by setting
coefficient g in Equation (1) and Equation (2) variably.
[0048] Next, when IM unbalance compensation computation section 306
converts an unbalance IM characteristic to a compensation
characteristic and generates a compensation signal, IM unbalance
compensation computation section 306 performs conversion to a
compensation characteristic so that there is symmetry with the
unbalance IM characteristic with respect to a fixed value at which
amplitude and phase become almost fixed when amplifier 312 is
assumed to have a linear characteristic. Specifically, the
compensation characteristic is obtained from Equation (3) using the
unbalance IM characteristic and linear characteristic found from
Equation (1) or Equation (2). Compensation
characteristic=Li.sub.--amp/Real.sub.--amp (3) where [0049]
Real_amp(t): Unbalance IM characteristic at time t [0050] Li_amp:
Fixed value
[0051] In this way, IM unbalance compensation computation section
306 converts the hysteresis characteristics shown in FIG. 6 and
FIG. 7 to the compensation characteristics shown in FIG. 8 through
FIG. 11. FIG. 8 and FIG. 10 are drawings showing the relationship
between amplitude and power in compensation characteristics, and
FIG. 9 and FIG. 11 are drawings showing the relationship between
phase and power in compensation characteristics.
[0052] By converting an unbalance IM characteristic to a
compensation characteristic, when input power is on an upward
trend, relationship #601 between amplitude and power is converted
to a relationship #801 between amplitude and power, and
relationship #701 between phase and power is converted to a
relationship #901 between phase and power. Also, by converting an
unbalance IM characteristic to a compensation characteristic, when
input power is on a downward trend, relationship #602 between
amplitude and power is converted to a relationship #802 between
amplitude and power, and relationship #702 between phase and power
is converted to a relationship #902 between phase and power. IM
unbalance compensation computation section 306 stores compensation
characteristics by storing the relationships between amplitude and
power and the relationships between phase and power shown in FIG. 8
through FIG. 11 in a data table as vector information.
[0053] That is to say, relationship #801 between amplitude and
power and relationship #802 between amplitude and power are
symmetrical with relationship #601 between amplitude and power and
relationship #602 between amplitude and power with respect to a
relationship #803 between amplitude and power in which amplitude
becomes almost fixed when amplifier 312 is assumed to have a linear
characteristic. Also, relationship #901 between phase and power and
relationship #902 between phase and power are symmetrical with
relationship #701 between phase and power and relationship #702
between phase and power with respect to a relationship #903 between
phase and power in which phase becomes almost fixed when amplifier
312 is assumed to have a linear characteristic.
[0054] Then, if measured power P(t) at time t has risen above
measured power P(t-1) at time t-1, IM unbalance compensation
computation section 306 determines that measured power is on an
upward trend, selects A1(t-1) as the amplitude component of
measured power P(t-1) at time t-1 and selects A1(t) as the
amplitude component of measured power P(t) at time t from FIG. 8,
and also selects .theta.1(t-1) as the phase component of measured
power P(t-1) at time t-1 and selects .theta.1(t) as the phase
component of measured power P(t) at time t from FIG. 9. IM
unbalance compensation computation section 306 then outputs a
compensation signal that has compensation characteristics for the
selected amplitude and phase components. The fixed value here is
found from relationship #803 between amplitude and power in which
amplitude becomes almost fixed as shown in FIG. 8 and relationship
#903 between phase and power in which phase becomes almost fixed as
shown in FIG. 9.
[0055] On the other hand, if measured power P(t) at time t has
fallen below measured power P(t-1) at time t-1, IM unbalance
compensation computation section 306 determines that measured power
is on a downward trend, selects A2(t-1) as the amplitude component
of measured power P(t-1) at time t-1 and selects A2(t) as the
amplitude component of measured power P(t) at time t from FIG. 10,
and also selects .theta.2(t-1) as the phase component of measured
power P(t-1) at time t-1 and selects .theta.2(t) as the phase
component of measured power P(t) at time t from FIG. 11. IM
unbalance compensation computation section 306 then outputs a
compensation signal that has compensation characteristics for the
selected amplitude and phase components. The fixed value here is
found in the same way as in the case of FIG. 8 and FIG. 9.
[0056] Next, complex multiplication section 307 suppresses
distortion component #203 and distortion component #204 in FIG. 2
by combining the transmit signal and compensation signal.
[0057] Here, the data table stored by IM unbalance compensation
computation section 306 is stored as vector information, and the
vector information has amplitude information and phase information.
Therefore, IM unbalance compensation computation section 306 has
amplitude and phase components corresponding to power P input to
amplifier 312 as a compensation data table. That is to say, the
relationship between an input signal to amplifier 312 and an output
signal from amplifier 312 is expressed as shown in Equation (4).
Output signal=amp.times.input signal (4) where amp: Amplifier
characteristic
[0058] Also, amplifier characteristic amp is expressed as shown in
Equation (5). amp(P)=A(P).times.e.sup.-j.theta.(P) (5) where [0059]
A(P): Amplitude component [0060] .theta.(P): Phase component [0061]
P: Power input to amplifier 312 [0062] amp(P): Amplifier
characteristic
[0063] Therefore, the amplifier characteristic can be found as an
amplitude component and phase component from Equation (5).
[0064] Thus, according to this embodiment, baseband signal
distortion components are suppressed by finding a compensation
signal that has an amplitude component and phase component that
differ when measured power is on an upward trend and when measured
power is on a downward trend, enabling distortion components in a
state of lower/upper unbalance to be suppressed with high
precision. Also, according to this embodiment, distortion
components in a state of lower/upper unbalance can be suppressed by
correcting linear characteristic information found by means of a
compensation data table 304 identical to a conventional
compensation data table 104 and a method identical to the
conventional method, and a conventional apparatus need not be
greatly changed, enabling an apparatus with good distortion
suppression precision to be provided at low cost.
[0065] As described above, according to the present invention
distortion components in a state of lower/upper unbalance can be
suppressed with high precision.
[0066] This application is based on Japanese Patent Application No.
2002-365447 filed on Dec. 17, 2002, the entire content of which is
expressly incorporated by reference herein.
INDUSTRIAL APPLICABILITY
[0067] The present invention relates to a distortion compensation
apparatus and distortion compensation method, and is suitable for
use, for example, in a distortion compensation apparatus and
distortion compensation method that eliminate distortion generated
when a signal is amplified.
* * * * *